Thread Challenge! Fix (and discuss) Perspective!

Canon EF 17-40mm f/4.0 L USM

01/14/2005 03:40:57 PM · #1

I have always been a little "shy" of doing perspective correction. When I do it, I don't save it unless I like the results, but the question is always there:

Does removing lens perspective distortion make it more "real" or less real?

So in anticipation of the Architecture challenge, I wanted to start a good discussion on this. Not so much focused on the tools (I saw a short thread about that, and I've tried a number of tools already), but on the subjective, and artistic side--how much should you correct?

I thought this image might present an interesting challenge. It's taken in RAW, with my Sigma 18-125 at 18mm, F7.1, 1/160. Pointing up slightly.

Anyone who wants to play, download this and do what you think should be done to perspective correct. Here's a link to a 1024x683 reduced photo--basically converted from raw and sharpened (since that's not done at all by the camera):
Download Photo

Here's a smaller upload of the photo (this one is converted from raw but not sharpened):

Here's my "entry" into the "thread challenge". (Hey, I get to play too...)

For this, I used DCE tools to do the correction, and then a final tweak using PS's skew. I can't really decide if this is quite "right", but I'll wait and see what others do. (Note: this was done on the unsharpened image. After I decided to make this a challenge I decided to do a little "presharpening" because a raw image from the 300d is so soft.)

Message edited by author 2005-01-14 15:43:21.

soup

Canon EOS-30D

01/14/2005 03:51:14 PM · #2

personally i prefer the distortion in most photos. i think in this example the un-corrected version is much more dynamic, and interesting.

not going to mess with it, as i should be working now...
but today i am mainly working on making the clock spin faster... it isn't working.

TechnoShroom

Canon EOS-30D

Canon EF 100mm f/2.8 USM Macro

01/14/2005 03:58:50 PM · #3

Originally posted by soup:

but today i am mainly working on making the clock spin faster... it isn't working.

Try drinking. Doesn't make the clock spin faster but you enjoy the hours more.

soup

Canon EOS-30D

Canon EF 17-40mm f/4.0 L USM

01/14/2005 04:08:57 PM · #4

does grapejuice count?

GeneralE

Canon PowerShot S3 IS

Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)

01/14/2005 04:14:02 PM · #5

Originally posted by soup:

does grapejuice count?

Once pre-digested by yeast it enjoys an increased "complexity."

Prof_Fate

01/14/2005 04:22:19 PM · #6

Since perspective adjustments 'move' pixels, it is not legal in the rules, basic or advanced.

So if you use it (aka cheat) and get a DQ request you will be DQ'd.
If you use it and get a ribbon, you will lose it upon verification.

based on the new rules, getting a DQ can have long term ramifications.

I know, this is not discussed in the rules, specifically. The 'moving' of pixels is not mentioned either. BUT it has been covered a number of times in the forums and apparently is not legal.

01/14/2005 04:28:50 PM · #7

Originally posted by Prof_Fate:

There has been discussion in the forums, but it was some time ago. Perspective correction does "move pixels", however it is legal under the advanced rules, if it's used to correct perspective, not to introduce an exaggerated "artistic" effect. Other tools that move pixels but would be deemed legal under the advanced rules are:
- Lens distortion correction
- Lens CA correction (moves pixels on one or two channels)
- De-fishing of images from fisheye lenses

01/14/2005 04:39:54 PM · #8

Here's my take...

I first applied lens distortion correction using PTLens, and then used PanoTools "perspective" tool to correct the perspective distortion. I used a FoV calculator to determine the proper FoV for the photo, and then tried different iterations of angle, settling on -12 degrees. It's still a little undercorrected, but I found this iteration overall the most pleasing.

01/14/2005 04:54:37 PM · #9

Originally posted by Prof_Fate:

Well this is a bit of a tangent to my thread challenge, but, where in the advanced rules does it say you can't move pixels? (I just searched the page but didn't find anything) The rules seem to be more correctly focused on the effect of any filter/change. If subject integrity is maintained, why would that be illegal? And it seems to me the rules still say you can use filters, including subtle artistic ones, which may move pixels, but that voters may frown on that.

Personally, I think perspective correction should be allowed in basic challenges as well, as long as you are fixing lens distortion!

Prof_Fate

01/14/2005 04:59:26 PM · #10

I just re-read the rules for both advanced and basic...neither mention moving pixels or lens'perspective correction etc.
In basic is states the adjustment must effect the entire image - which perspective correction does (or can/should)

Since the basic rules do not prohibit it, it must be legal. THe discussion //www.dpchallenge.com/forum.php?action=read&FORUM_THREAD_ID=120366&highlight=perspective%20correction
here seems to state the SC's opinion, but it was not included in teh new ruleset.

There have been other threads on this general topic. I just find it confusing that it is not mentioned in the rules in any way- that to me implies it is legal(both advanced and basic). I just don't want to wake up with a ribbon (i mean I [b]do[/b want to) only to find out becuse i have not read and remembered every thread ever written I am going to be DQ'd.

see also
//www.dpchallenge.com/forum.php?action=read&FORUM_THREAD_ID=150017&highlight=perspective%20correction
//www.dpchallenge.com/forum.php?action=read&FORUM_THREAD_ID=141364&highlight=perspective%20correction

01/14/2005 04:59:45 PM · #11

Originally posted by kirbic:

Here's my take...

I first applied lens distortion correction using PTLens, and then used PanoTools "perspective" tool to correct the perspective distortion. I used a FoV calculator to determine the proper FoV for the photo, and then tried different iterations of angle, settling on -12 degrees. It's still a little undercorrected, but I found this iteration overall the most pleasing.

The one aspect you really nailed here is the pole versus the building. In my playing around, I never quite got that right. But while the building has really nice straight lines for perspective, it subjectively looks 'wrong" to me. This is the question I always ponder: if you fix the perspective, will the scene look more 'real' or 'wrong'?

In this case, **very subjectively**, the building looks to be reverse perspective distorted: too tall, and very slightly bowing out at the top (which may simply be a perspective illusion).

Fritz, I have panotools but haven't tried it yet for this because it requires numerical input rather than being interactive, like the other tools I tried. But it looks like you had some other tools to help: where did you get the FOV calculator you used to gen the numbers?

Thanks for playing ;)

Nikon AF-S Nikkor 28-300mm f3.5-5.6G ED VR

01/14/2005 05:18:23 PM · #12

Neil,
I agree 100% regarding the subjective aspect of this type of correction. Very often the "correct" result just looks jarring. I think that's part of why leaving this undercorrected looked better to me.
For the FoV calculation I used a very simple Excel spreadsheet that I wrote myself. e-mail me if you want a copy.
Also, for completeness, PTLens

Message edited by author 2005-01-14 17:18:38.

scottwilson

Canon EOS-350D Rebel XT

Canon EF 28mm f/2.8

01/14/2005 05:21:33 PM · #13

Here is my try.

Arcanist

Nikon D810

01/14/2005 05:38:25 PM · #14

Perspective Crop with PScs.
Resize Image without constrain to orginal pixels.

mrorange002

Canon EOS-5D

Canon EF 16-35mm f/2.8 L USM

01/14/2005 05:59:07 PM · #15

this looks good to me:

eggv

Canon EOS-1D Mark IIn

Canon EF 24-70mm f/2.8 L USM

01/14/2005 06:06:27 PM · #16

Our cut at it

Gringo

Nikon D2X

Nikon AF-S Zoom-Nikkor 28-70mm f/2.8D IF-ED

01/14/2005 07:40:54 PM · #17

;)

Message edited by author 2005-01-14 22:06:55.

01/14/2005 07:41:40 PM · #18

Well I have to say, Eric's version is quite compelling. Eric did you use the "J.Daniels" filter on that? ;)

I could offer my opinion on the others (which I think are quite good), but I was also curious what others visiting think? What looks natural and best to you?

Canon EF 16-35mm f/2.8 L USM

01/14/2005 08:12:38 PM · #19

Neil, your comment regarding numeric vs. interactive input gave me an idea. This take...

...was the result. This is actually corrected interactively with Panotools/PTGUI. It's corrected in two directions, not just one, and I think the results are much better. I also was able to avoid losing so much of the pic during correction. I'll never do correction in PS again!
Oh, yeh, here's the method...
- Do lens distortion correction (in PS using PTLens)
- Save file
- Open file in PTGUI/PanoTools. PTGUI should read the EXIF and enter it's own lens parameters. You'll need to verify that they are correct.
- Open the panorama editor, and move the pic around within the fame until it looks correct.
- Verify output options and "create panorama". Remember to click "set optimum size" button. Click OK when you get the "optimizer has not been run" error dialog.

Message edited by author 2005-01-14 20:30:45.

mrorange002

Canon EOS-5D

01/14/2005 08:18:28 PM · #20

Originally posted by nshapiro:

Actually Hornito's ;D

No kids tonight!!!

(thank goddess for grandparents)

Bear_Music

Samsung Galaxy S24, S24+, S24 Ultra

Sony Vario-Tessar T* FE 24-70mm f/4 ZA OSS

01/14/2005 09:09:09 PM · #21

Speaking "professionally", the original shot would never be published by any "shelter" or arcitetcure publication. Minimum competence requirement, in their books, is true verticals, with rare excepotions that are extremely distorted deliberately.

I'm sensitive to the fact that "lay indviduals" may find a distorted view more natural, but architects would not. It's all in the training and visualization-set we acquire, I think. Inidentally, these "corrections" are basically acquired in the camera when you use a large-format camera. Or, more to the point, the deviations are never introduced. If anyone wants to know why that is, I'd be glad to explain.

Robt.

01/14/2005 09:24:50 PM · #22

Yeh, but tilt/shift lenses are pretty far down our acquisition lists... not off of the lists, mind, but pretty far down.